Method for checking or calibrating the angle-dependent alignment of a high-precision test-piece

ABSTRACT

The invention related to a method for checking or calibrating the angle-dependent alignment of a reference structure on a high-precision test-piece. After arrangement of the test-piece on a retainer piece, a pre-alignment of an optical unit and/or the reference structure of the test-piece is carried out, such that the test-piece beam is at least partly incident on a detector and generates at least one point there. The position of the at least one point on the detector is evaluated by means of a control/regulation unit. After a relatively fine alignment of the optical unit relative to the reference structure, by means of the control/regulation unit, depending on the position of the at least one point on the detector, such that the at least one point has a given set position on the detector, a recording of at least the retainer piece rotation angle and/or the measuring piece rotation angle is carried out, whereby a beam from the reference structure of the test-piece is generated, or modified with relation to a beam parameter, in particular, by reflection, stopping, filtering or shaping and the generated or altered beam forms the test-piece beam.

The invention relates to a method for checking or calibrating theangle-dependent alignment of a high-precision test piece.

For checking or calibrating high-precision parts which either serve forhighly accurate measurement, checking or specification of angles with aprecision down to less than 0.5″ or 0.15 mgon or generally requirehighly accurate angle orientations, very high-precision checking orcalibrating devices are required, the accuracy of which must be evenhigher than that of the high-precision test pieces to be checked orcalibrated.

Particularly for checking or calibrating a theodolite, in which ahorizontal and a vertical angle are determined by—for example static ordynamic—indexings, different devices and methods are disclosed in theprior art.

In a classical theodolite indexing test method known for a relativelylong time, a plurality of stationary collimators distributed about thestation are sighted manually with the theodolite telescope from a fixedstation. The constancy of the angle differences measured at variouspoints of a circle around the test piece, is used as a measure of thehorizontal accuracy of angle measurement. For the vertical accuracy ofmeasurement, the collimator angle differences are compared with thereference values. Reference circle testers to carry out such a referencecircle test method are known (e.g. PRUTE and PRUFO devices from F. W.Breithaupt & Sohn). Such methods correspond substantially to the testmethod according to ISO standard 17123-3 (Optics and opticalinstruments—Field procedures for testing geodetic and surveyinginstruments), but fixed targets instead of collimators are sightedthere. Disadvantages of these theodolite indexing test methods are,inter alia, that complete automation of the measuring process ispossible only to a limited extent, the number of possible differentmeasurements is limited to the number of sightable collimators and theresult of the measurement is greatly dependent on the observer.

An alternative to the above mentioned method is the interferometric testmethod of Maurer (Maurer, W.: Ein interferometrisches Verfahren zurBestimmung von Strichverbesserungen an eingebauten Theodlitenkreisen [Aninterferometric method for determining line improvement on built-intheodolite circles]; Thesis Munich, 1983; Deumlich, F. & Staiger, R.:Instrumentenkunde der Vermessungstechnik [Instrument theory of surveyingtechnology]). In this method, the angle through which the theodolite tobe tested is rotated is derived from the path difference of a laser beamto interferometer reflectors. The maximum interferometrically measurableangle is +/−8.5 gon, and the resolution is stated as 0.01 mgon. Onlychecking of horizontal angles is possible with the interferometricmethod. This method is unsuitable for checking vertical angles since itwill be necessary for a prism holder to be rotatably connected to thetilting axis of the theodolite, making it impossible to rule out aninfluence on the vertical indexing and the tilting axis because of theadditional weight of the prism holder.

Test methods for checking of a removed reference circle, for example ofa theodolite, are known from the prior art. These methods are chieflycomparison methods in which the indexing to be checked on the referencecircle is compared with a correspondingly accurate angular normal, forexample interferometrically or by means of a precision reference circle.Different devices of this type, which are used, for example, in thePhysikalische Technische Bundesanstalt (Prowe, B.: Untersuchungen aneinem neuen Teilkreisprüfgerät [Investigations into a new referencecircle tester]; Feinwerktechnik & Messtechnik, Issue 5, 1985, pages213-217) or at the Zentralinstitut für Physik der Erde (Weise, H. &Quart, W.: Eine vollautomatische Messanlage zur Prüfung vonKreisteilungen [A fully automatic measuring unit for checking circlegraduations]; Feingerätetechnik, Issue 4, 1975, pages 155-160), orfurther devices for checking reference circle graduations, for examplefrom CH 372847 or CH 372471, are disclosed in the prior art. In the caseof these methods and devices, however, no indexing test of a mountedtheodolite is possible but only checking of a removed reference circle.In addition, reference may be made to ISO standard 17123-3 (Optics andoptical instruments—Field procedures for testing geodetic and surveyinginstruments) or DIN 18723, Part 3 (Feldverfahren zurGenauigkeitsuntersuchung geodätischer Instrumente [Field methods forinvestigating the accuracy of geodetic instruments]).

A device and a method for fully automatic checking and calibration of atheodolite, of a tacheometer or of a total station, summarised below bythe term “theodolite”, is disclosed in the prior art. This so-called“theodolite test machine” is described in detail, for example, in thearticle “TPM—Ein neues Gerät zur vollautomatischen Prüfung vonTeilkreisen in elektronischen Theodoliten [TPM—A new device for fullyautomatic checking of reference circles in electronic theodolites]” byHilmar Ingensand for the X. International Course for EngineeringSurveying at the Technical University of Munich on Sep. 12-17, Sep. 1988and in the diploma thesis “Kalibriereinrichtung für Theodoliten[Calibration device for theodolites]” by Andreas Rützler, implemented atthe Institute for General Electrical Technology and ElectricalMeasurement Technology of the Technical University of Graz in October1991. The theodolite test machine has an accuracy of about 0.1 mgon andserves, for example, for checking electronic theodolites with a codedreference circle indexing system which immediately outputs an anglewithout the initialisation otherwise necessary in incremental methods,but has only a single angle indexing instead of diametrical scanning ofthe reference circle. The error generated here by the mechanicaleccentricity of the reference circle is specific for each theodoliteand, after measurement with the theodolite test machine, can be storedin the electronic theodolite and automatically corrected. The theodolitetest machine permits a fully automatic test sequence, for checking ofhorizontal and vertical angle indexings in the position of use in theinstalled state, checking over a major part of the usable measuringrange of the theodolite, the analysis of the systematic errorsdetermined in the test procedure and the automatic determination of acorrection function, which is stored in the theodolite. The theodolitetest machine is suitable for different theodolite series.

This theodolite test machine disclosed in the prior art is described inmore detail below with the aid of figures.

FIG. 1 shows the comparator concept of the theodolite test machinedisclosed in the prior art;

FIG. 2 shows the device setup of the theodolite test machine disclosedin the prior art.

The known theodolite test machine, which is based on the comparatorconcept shown in FIG. 1, follows the idea of a “theodolite in atheodolite”. The system of axes of the theodolite test machine thuscorresponds geometrically to that of the theodolite to be testedresulting in a substantially common system of axes with a vertical axis101 and a horizontal axis 102. The theodolite is shown schematically inthe form of an alidade 103, which is rotatable about the vertical axis101 relative to a lower part 104 of the theodolite, and of a telescope105 tiltable about the horizontal axis 102 and having a sighting axis106. Since absolute centring of the system of axes of the theodolite tobe checked and of the theodolite test machine is ruled out, the anglemeasuring systems, the normal of the theodolite test machine and theindexing of the theodolite are coupled by means of an autocollimator 107pivotable about the horizontal axis 102. The coupling is effected bymeans of a collimated beam 113 via a planar mirror attachment 108 fixedon the telescope 105. Since the theodolite test machine and thetheodolite fulfil the condition of orthogonality of the axes (101, 102,106) all systems of axes are collinear in the autocollimation setting.According to the design of theodolites, the sequence of the horizontaland vertical check is different. In the horizontal check, the alidade103 of the theodolite to be checked remains substantially fixed and thelower part 104 which is mechanically connected to the angular normal, isrotated about the vertical axis 101. After a coarse setting of the testangle by rotation of the lower part 104 of the theodolite relative tothe substantially stationary alidade 103, a fine adjustment of the testangle is made by means of autocollimation by rotating the lower part 104and the alidade 103 together with high-precision and optionally slightlypivoting the autocollimator 107, with the result that the theodolite andthe normal are brought into reference. The horizontal positions aredetermined by very high-precision horizontal indexing 109 of thetheodolite test machine and horizontal indexing 110 of the theodoliteand are compared. The vertical checking is effected by pivoting theautocollimator 107 in the common vertical plane about the horizontalaxis 102 and hence about the theodolite to be checked. The telescope 105of the theodolite is also coarsely rotated through the specified angle.After the subsequent autocollimation adjustment, the vertical positionof the autocollimator 107 is determined by very high-precision verticalindexing 111 of the theodolite test machine and the vertical position ofthe telescope 105 is determined by vertical indexing 112 of thetheodolite and said positions are compared.

FIG. 2 shows the device design of the known theodolite test machinehaving a vertical axis 121 and a horizontal axis 122. The design isequal to that of a 3-D coordinate measuring machine with respect to thestability requirements in the μ range, which is why a granite frame 123is used as a retainer of the systems of axes. The entire machine restson a concrete foundation (not shown) and is erected in an airconditioned room. A horizontal measuring part 124 which is similar to aprecision turntable and is mounted by means of roller bearings 125 andis rotatable about the vertical axis 121 by means of a horizontal drive126 is fixed on a base plate 123′. The horizontal measuring part 124also has a horizontal angle sensor 127. A tripod 129 for retaining atheodolite 130 to be checked is mounted on the horizontal measuring part124. The electrical connection for the attached theodolite 130 is madeby means of a slip ring system (not shown). A vertical measuring part131 has a measuring bridge 134 which is pivotable about the horizontalaxis 122 and driveable by means of a vertical drive 132, has a verticalangle sensor 133 and carries an electronic autocollimator 135. Afork-like driver 136 which serves a stop for a telescope 137 of thetheodolite 130 is also arranged on the measuring bridge 134. Thus, thevertical position of the telescope 137 substantially follows that of theautocollimator 135. However, since the driver 136 has a play relative tothe telescope 137, the driver 136 and the telescope 137 are decoupledduring fine adjustment of the measuring bridge 134. In the same way, thedriver 136 serves as a stop in the case of horizontal adjustment bymeans of the horizontal measuring part 124. The stability of the heavymeasuring bridge 134 is critical since, particularly in the horizontalposition, high bending movements which may falsify the measurement acton the structure of the measuring bridge 134. The U-shaped measuringbridge 134 is mounted on both sides on the granite frame 123, by meansof tilting axis bearings 138 in the form of pretensioned ball/sleevebearings, so as to be rotatable about the horizontal axis 122. In orderto relieve these tilting axis bearings 138 from radial forces exerted bythe weight of over 12 kg of the measuring bridge 134 and the electronicautocollimator 135 themselves, the machine has an additional weightcompensation system. The entire measuring bridge 134 is supported at thecentre of gravity by an outer bearing frame 139 which also carriescounterweights 140 and takes up the drive forces. This bearing frame 139rotates in its own separate bearing frame bearings 141. Theautocollimation adjustment is effected by the autocollimator 135 of thetheodolite test machine projecting a collimated light beam on to aplanar mirror attachment 142 which is attached to the telescope 137 ofthe theodolite 130 normal to the direction of the sighting axis of thetelescope 137. The mirror attachment 142 is fixed on the telescope 137by a collet (not shown). It is thus possible to mount the mirrorattachment 142 substantially normal to the optical axis of the telescope137 and hence to the sighting axis. The mirror attachment 142 reflectsthe collimated light beam back into the autocollimator 135 of thetheodolite testing machine. The light beam strikes a position detector(not shown), which is in the form of a quadrant diode, at the focalpoint of the autocollimator 135 and produces a light spot there. Theresolution of the autocollimator 135 is about 0.01 mgon. The horizontalmeasuring part 124 with the theodolite 130 and the measuring bridge 134with the autocollimator 135 are precisely moved by the horizontal drive126 and the vertical drive 132, respectively, which have 15 V DC motorswhich can be activated with pulse width modulation, until the light spotis present in the middle of the position detector of the autocollimator135. In addition, a coarse/fine reduction (not shown) in the ratio 1:9permits the required very fine positioning of the control loop whichcomprises the electronic autocollimator 135, a computer (not shown)including control software, and the mechanical drives 126 and 132. Thesystems of axes of the theodolite 130 and of the theodolite test machineare thus substantially collinear after the autocollimation adjustment.The computer performs the control of the measuring sequence, theregulation of the target adjustment and the evaluation of the results ofthe measurements.

The sequence of the vertical and horizontal measuring process isdescribed below. The measuring bridge 134 is brought into anapproximately horizontal position before the theodolite 130 to bechecked is attached, so that the autocollimator 135 is presentapproximately in the vertical position 100 gon, measured from thezenith, towards which the vertical axis 121 points. The theodolite 130is fixed on the tripod 129 of the horizontal measuring path 124 with thevertical axis pointing in a perpendicular direction, so that thevertical axis of the theodolite 130 and the vertical axis 121 of thetheodolite test machine coincide as far as possible but are at leastcollinear. The planar mirror attachment 142 is fixed on the objective ofthe telescope 137 of the theodolite 130 by the collet. The telescope 137is pivoted into the fork-like driver 136 of the measuring bridge 134. Atthe beginning of the measurement, the measuring bridge 134 moves to thevertical position 260 gon, measured from the zenith, the beginning ofthe vertical measuring range. The driver 136 carries the telescope 137of the theodolite 130 with it during this movement. By the subsequentautocollimation adjustment, the autocollimator 135 is aligned with themirror attachment 142 fixed on the telescope 137 by a precise adjustmentof the measuring bridge 134 and of the horizontal measuring part 124.Owing to the play between driver 136 and telescope 137, the telescope137 is not put out of adjustment by the driver 136 during theautocollimation adjustment. After this autocollimation adjustment, theangle values of the theodolite 130 and those of the theodolite testmachine are polled by the computer and stored. The difference betweenthe vertical angles is the error of the theodolite 130 for therespective vertical position, in this case 260 gon. The measurement ofthe first measuring point is herewith complete. For the measurement ofthe next measuring point, the vertical drive 132 of the theodolite testmachine moves the measuring bridge 134 and, by means of the driver 136,also the telescope 137 of the theodolite 130 through about 15 gon to thevertical position 275 gon. The measurement of the second point accordingto the scheme described above now begins. In this way, verticalmeasurements up to the vertical position 140 gon are carried out, therange from 380 to 20 gon close to the zenith being omitted since, inthis range a possible offset of the test piece and of the theodolitetest machine axes can scarcely be corrected or cannot be corrected bythe horizontal drive 126 of the theodolite test machine. This is becausethe horizontal movement of the light spot on the position detector ofthe autocollimator 135 in relation to the vertical angle of rotation islinked to the tangent of the angle between the horizontal position andthe actual position of the measuring bridge 134. After the end of thevertical checking, the measuring bridge 134 is moved to the verticalposition 100 gon and the investigation of the horizontal indexing of thetheodolite 130 is begun. The theodolite 130 is rotated in one directionby means of the horizontal measuring part 124, the lower part 143 andthe alidade 144 of the theodolite 130 moving together until thetelescope 137 of the theodolite 130 strikes the stop of the fork-likedriver 136 and is held, with the result that the alidade 144 stops andonly the lower part 143 is moved onwards. Once the desired horizontalangular position of the theodolite 130 has been reached, the horizontalmeasuring part 124 is rotated slightly in the opposite direction, withthe result that the telescope 137 is rotated away from the driver 136and hence no mechanical stop hinders the adjustment process during theautocollimation adjustment. After the autocollimation adjustment, themeasured values are recorded analogously to the vertical measurement. Inthe horizontal investigation, about 35 points distributed uniformly overthe circumference are measured. After the end of the entire horizontaland vertical checking process, the stored pairs of angles are evaluated.

This known theodolite test machine has numerous disadvantages andproblems which could not be adequately solved to date. Since themeasuring bridge bearing the autocollimator is subjected to high bendingmoments in the horizontal position by its own weight and the weight ofthe autocollimator, the measuring bridge must have a stable design sothat any deformation of the measuring bridge which falsifies themeasurement is as far as possible avoided. However, the weight of themeasuring bridge should not be too high since, within the specifiedtolerances, the load-bearing capacity of the high-precision tilting axisbearing which supports the measuring bridge on the granite frame isgreatly limited. For static reasons, in particular in order to avoiddeformations and to load the tilting axis bearing as little as possible,a U-shape with tilting axis bearings on both sides appears to beadvantageous and in turn requires a twin-column granite frame. Owing tothe limited load-bearing capacity of the tilting axis bearings in theform of pretensioned ball/sleeve bearings, the high weight of themeasuring bridge also requires a complicated weight compensation system,which further increases the total weight of the theodolite test machine.The solid granite frame required owing to the tilting axis bearing onboth sides and surrounding the measuring bridge, the U-shape of themeasuring bridge and the weight compensation system severely-limit theaccessibility of the theodolite to be checked, which is a hindranceparticularly during adjustment work and in the case of large testpieces. The solid structure and the weight of the known theodolite testmachine prevent broad potential use since firstly load tolerances ofnormal industrial floors are exceeded and secondly the theodolite testmachine cannot be transported through the normal laboratory doors. Owingto the arrangement of the tilting axis bearings on both sides,stress-free, exact adjustment of the individual tilting axis bearings isvery problematic because of static over determination, since themisadjustment of a tilting axis bearing always also acts on the oppositetilting axis bearing, with the result that the high precisionrequirements can be met only where there is considerable adjustmenteffort. The stable mounting of the mirror attachment on the telescope isalso critical since deviations from the mirror plane relative to thetarget axis should as far as possible be avoided, and exact alignment ofthe mirror attachment requires a considerable effort. Differenttelescope geometries and theodolite model ranges require differentmirror attachment collets. Since the reference structure for the entiremeasuring sequence is formed by the mirror attachment, only the anglesensors and the axes of the theodolite can be checked. Errors in thetelescope optical system are thus not taken into account. Only thealignment of the mirror attachment is detectable by means of theautocollimator used, but not the position and quality of individualstructures of the telescope optical system, such as, for example, thequality or alignment of individual lenses, of a beam splitter cube, ofan image recording area or of the line of the tube. Checking of anylaser telemeter integrated in the theodolite cannot take place since themirror attachment obscures the telescope optical system. Furthermore,the inclinometer in the theodolite cannot be calibrated using the knowntheodolite test machine. The development of new and even more precisetheodolites moreover requires an even higher accuracy of the theodolitetest machine.

SU 763682 A discloses a manually operated apparatus for checking ageodetic device which has in particular a sighting apparatus tiltableabout an axis of rotation in a vertical plane. A stationary calibrationcollimator of long focal distance with an ocular micrometer ispositioned on a frame, which is present on a table, in such a way thatthe collimator axis coincides with the axis of rotation of the sightingapparatus—the tilting axis—of the device to be investigated, which islikewise installed on the table. The device to be investigated can beinclined and horizontally aligned by means of a non-rotatable liftingapparatus. A rotating block which is mounted on one side and acts as ameasuring frame for the vertical angle check and the axis of rotation ofwhich coincides with the collimator axis—and therefore in particularwith the tilting axis of the device to be investigated—and which has apassage for allowing through collimator beams is arranged between thecalibration collimator and the device to be investigated. The heavyrotating block equipped with a plurality of counterweights comprises anoptical system which deflects the beam in such a way that it is firstdisplaced parallel by a certain offset, which is not less than theexternal dimension of the largest device to be checked, and which thendeflects the beam which has been displaced parallel by 90° in the planeof the parallel offset, the deflection being achieved by means of apentaprism at the point of intersection of the axis of the displacedbeam with the vertical plane of the tiltable sighting apparatus of thedevice to be investigated. A small opening through which a part of thecollimator beam can pass without reflection or deflection is provided onthe first reflecting surface of the optical system of the rotatingblock. The rotating block is equipped with a highly accurate limbus andan angle reading apparatus. If the device to be investigated is atheodolite, it is possible by means of the apparatus, by swivelling therotating block, to check the vertical angle measuring apparatus of thetheodolite and to generate a mathematical error correction function.Owing to the stationary theodolite, horizontal angle correction ispossible for not more than four horizontal angles only by penetration ofthe theodolite telescope, so that it is not possible to realise acontinuous horizontal angle correction function. The alignment of thetheodolite telescope with the rotating block and vice versa is carriedout by the user viewing either the collimator net in the theodolitetelescope or the theodolite net in the collimator telescope with the eyeand manually adjusting the axes. The calibration of the entire apparatusis carried out with the aid of the autocollimator eyepiece of thecollimator by arranging a calibration prism or a polygonal mirror on thetable and measuring the constancy of the position of the optical axis ofthe apparatus at different positions of the rotating block. Since theapparatus has a nonrotatable retainer apparatus for the theodolite, itis not possible to check a plurality of horizontal angles within ameasuring process. It is therefore not possible to determine acorrection function obtained from a multiplicity of horizontal anglemeasurements and store said correction function in the electronictheodolite for automatic error correction. Since only the collimator netor the theodolite net serves as a reference for the check, it is notpossible to check or to calibrate individual structures, for example,lens surfaces, beam splitter cubes, image recording area or a lasertelemeter with respect to the alignment and position. Since, in thisapparatus, the calibration collimator is arranged far away from thedevice to be investigated, in such a way that the collimator axiscoincides with the axis of rotation or tilting axis of the device, acomplicated beam guidance system susceptible to error and comprising aplurality of mirrors has to be arranged in the rotating block. This bothreduces the torsional rigidity and flexural strength of the rotatingblock and increases the weight of the rotating block and of the entireapparatus since heavy counterweights are required. Consequently, becauseof the system itself, it is not possible to meet very high accuracyrequirements down to below 0.5″ or 0.15 mgon with the device disclosed.However, the apparatus is distinguished by the easy accessibility of thedevice to be checked since access to the device can be gained from threesides. There is no possibility of carrying out a fully automaticcalibration process with the apparatus disclosed.

The object of the invention is to provide a universally usable testmethod by means of which the angle alignment and the quality ofindividual reference structures of different highly accurate testpieces, preferably geodetic measuring instruments, can be automaticallychecked and calibrated in a reliable and highly accurate manner, and toovercome the disadvantages of the test methods of the generic type.

This object is achieved by realising the features of the independentclaim. The features which further develop the invention in analternative or advantageous manner are described in the dependentclaims.

The invention is based on the concept that substantial improvementscompared with the prior art can be achieved by direct measurement on areference structure of the test piece.

The method according to the invention is described generally belowpartly with the aid of descriptions of the device. Possible specificexemplary embodiments are described after the figures and thedescription of the figures.

A possible device for checking or calibrating the angle-dependentalignment of a reference structure of a high-precision test piece has aplinth as a stable reference base for the checking or calibrationprocess.

This plinth is in the form of a stone body or metal body or in the formof a body which is manufactured from at least one other suitablematerial or composed, for example, of struts which serves as a referencebase. The plinth has, for example, a L-shaped basic structure. Aretainer part for retaining the test piece is mounted so as to berotatable relative to the plinth about a retainer part axis—running inthe perpendicular direction—by means of a high-precision bearing. Theretainer part may be, for example, in the form of a precision turntablehaving a holder optionally adjustable by means of a tripod and intendedfor retaining the test piece. An angle of rotation of the retainer partrelative to the plinth about the retainer part axis, referred to belowas angle of rotation of the retainer part, can be measured with highprecision, for example, by means of an angle encoder with dynamic orstatic indexing. If an exact absolute vertical alignment of the retainerpart or of the holder is required for checking or calibration, it isfurthermore possible to integrate a tilt sensor in the retainer part. Inaddition, it is possible to use means for inclining the retainer part orthe entire plinth. These means for inclination can be used either forexact vertical alignment, in particular of the retainer part or of thetest piece, or for checking a tilt sensor of the test piece. In the caseof electronic test pieces which require a voltage supply or transmitmeasured values, the rotatably mounted retainer part is moreoveroptionally equipped with means for electrical connection, for example aslip ring or rolling ring system, in order to permit an electricalconnection between the plinth and the test piece. Of course, radiotransmission systems, for example Bluetooth, infrared systems or similarsystems can also be used instead.

The device also comprises a measuring part which is mounted so as to berotatable relative to the plinth about a measuring part axisintersecting the retainer part axis at right angles. An angle ofrotation of the measuring part about the measuring part axis ismeasurable with high-precision, for example by means of an angle encoderwith dynamic or static indexing. The basic shape of the measuring partis formed so that the measuring part grips around the test piece by asubstantially mirror-symmetrical or axially symmetrical—for examplecollet-like—formation with respect to the measuring part axis from atleast two sides or fully encloses said test piece by a substantiallyrotationally symmetrical formation. The measuring part is rotatable atleast in a certain angular range independently of the test piece. Such asurrounding or enclosing, at least partly symmetrical formation of themeasuring part has several advantages. Since the centre of gravity ofthe measuring part is close to or on the measuring part axis, additionalweight compensation can be dispensed with. Consequently, the drive ofthe measuring part is relieved, the bending and torsional load isconsiderably reduced and hence the accuracy of the measurement isdramatically increased owing to smaller tolerances. A further advantageof such a design of the measuring part is the possibility of arranging aplurality of measuring components within the measuring plane of themeasuring part—in particular on opposite sides relative to the testpiece. This makes it possible to realise numerous novel measuringmethods, by means of which the accuracy of the measurement can befurther increased.

At least one optical unit having an optical detector is arranged on themeasuring part. The optical unit serves for receiving at least one testpiece beam which interacts with the reference structure of the testpiece and is substantially in a measuring plane through which themeasuring part axis passes perpendicularly and in which the retainerpart axis lies. As a result, the test piece beam produces at least onepoint on the detector. The test piece beam can either strike thedetector directly, possibly shaped by a lens system, or can be deflectedor conducted by an optical deflection element, for example a reflectingunit or an optical fibre, in the direction of the optical unit and ofthe detector and can strike the detector indirectly. With the use ofsuch an optical deflection element, it is possible to arrange theoptical unit outside the measuring plane, possibly on a sub element ofthe measuring part. The test piece beam interacting with the referencestructure of the test piece is to be understood generally as meaning abeam, for example a beam of light rays, which interacts directly orindirectly with at least one reference structure of the test pieceand/or arrives from such a part. The interaction between the test piecebeam and the reference structure takes place, for example, byreflection, scattering, refraction, beam shaping, stopping, filtrationor beam generation.

The term “test piece” means an element as a whole which is to be checkedor adjusted, for example a geodetic measuring instrument, a polygonalmirror unit or a mechanical high-precision part, without possibleauxiliary components mounted for carrying out the measuring process,such as, for example, a mirror attachment. The reference structure meansa test piece structure which is to be checked specifically with regardto the angular alignment or its quality. This may be, for example, abody, a surface, an edge or a point. In the case of a test piece havinga mirror surface which is to be exactly aligned or which is exactlyaligned relative to a base surface, the reference structure is formed,for example, by this mirror surface. In the case of a test piece in theform of a theodolite, the reference structure of the test piecerepresents, for example, a part of the horizontally and verticallyrotatable or tiltable telescope.

Both the retainer part and the measuring part are preferably capable ofbeing driven by an electric motor. Thus, based on the test piece, thereceiving area of the optical unit forms a section of a sphericalsurface which at least partly encloses the test piece, by adjustment ofretainer part and measuring part about the retainer part axis or themeasuring part axis. If the retainer part axis points in theperpendicular direction and hence the measuring part axis lies in thehorizontal plane, a horizontal angle can be adjusted by means of theretainer part and a vertical angle by means of the measuring part.

The rotatable mounting of the measuring part relative to the plinth iseffected by means of a measuring part bearing unit which is preferablyin the form of an air bearing, which is arranged on a single side of themeasuring plane or in the measuring plane. Since only one bearing unitis used, this bearing unit can be adjusted with high precision withoutresulting in warping with a second bearing unit mounted on the otherside of the measuring plane or outside the measuring plane, owing tostatic overdetermination. This makes it possible to achieve extremelyhigh accuracies of measurement. Because the bearing unit is arranged onone side and lies on a single side of the measuring plane or is arrangedcentrally and lies in the measuring plane, it is possible to realise amore compact, in particular narrower design of the entire measuringdevice and to provide substantially better accessibility to the testpiece, the accuracy of the measurement of the entire device even beingfurther increased owing to the properties of an air bearing. Differentdevelopments of radial and axial air bearings and cylindrical, U-shaped,angled or planar air bearings have in the meantime been disclosed in theprior art. The air bearing must be such that highly precise mounting ofthe measuring part about the measuring part axis, taking into theaccount the required tolerances of the device under the forces acting onthe bearing, is ensured and both the rigidity and the damping meet therequirements. The design criteria of air bearings have also beendisclosed in the prior art. The bearing unit in the form of an airbearing is to be understood as meaning both an individual bearing and anarrangement of a plurality of—in particular clamped—bearings in the formof a bearing unit. Of course, it is possible to use a conventionalsliding bearing or roller bearing or possibly a magnetic bearing insteadof an air bearing. In some of these cases, however, it is not possibleto achieve such small tolerances as in the case of an air bearing.

In addition, it is possible also to form the high-precision bearing ofthe retainer part as an air bearing.

The measuring part is optionally formed so that apart from the opticalunit, an additional optical unit is arranged on that side of themeasuring part which is opposite the optical unit with respect to themeasuring part axis. This additional optical unit may be, for example,in the form of an additional emitter, an additional mirror, anadditional autocollimator or an additional camera. Possible embodimentsof the measuring part are to be found in the description of the figures.

A control/regulation unit controls the device, in particular themotor-operated alignment of the optical unit relative to the referencestructure of the test piece by means of motor-operated adjustment of theretainer part and of the measuring part as a function of the position ofthe at least one point produced by the test piece beam on the detector,in particular also or alternatively as a function of a signal of anadditional optical unit. Acquired measured data, in particular those ofthe angle encoder, may be stored and/or evaluated. Thecontrol/regulation unit may be, for example, in the form of a personalcomputer having appropriate ports, a combination of controls orintelligent sensors and actuators, a PLC or a computer system connectedto a data network.

Particularly in the case of test pieces whose reference structure to bechecked or calibrated with respect to its angular alignment isadjustable relative to the remaining test piece, as is the case, forexample, with a theodolite whose angle encoders are to be checked, ahandling robot, which is arranged, for example, on the plinth, is usedfor adjusting the reference structure, for example of the theodolitetelescope. It is thus possible to adjust the reference structure and theoptical unit of the measuring part simultaneously and to determine angledeviations—in particular of an angle encoder of the test piece—within ashort test time.

For checking the thermal behaviour of a test piece, it is possible touse a thermal emitter which is arranged in such a way that the testpiece can be heated at least from one side, with the result that, forexample, the influence of sunlight and the associated thermal distortioncan be simulated.

In the method according to the invention, radiation is generated by thereference structure of the test piece or is modified with respect to aradiation parameter—in particular by reflection, filtration or shaping.This generated or modified radiation forms the test piece beam describedabove.

For carrying out the method according to the invention, it is possibleeither to use substantially the device described above or in general thefollowing device is used: the device comprises an adjustable or fixedretainer part for retaining the test piece and an adjustable measuringpart, the measuring part and the retainer part being rotatable relativeto one another about a retainer part axis and a measuring part axisintersection the retainer part axis at right angles. An angle ofrotation of the retainer part about the retainer part axis and an angleof rotation of the measuring part about the measuring part axis aremeasurable between the measuring part and the retainer part. The devicefurthermore has an optical unit arranged on the measuring part andhaving an optical detector for receiving at least one test piece beamwhich interacts with the test piece and lies substantially in ameasuring plane through which the measuring part axis passesperpendicularly and in which the retainer part axis lies, and producesat least one point on the detector. It is of course possible for theoptical unit with the detector to be arranged not directly on themeasuring part but on another part, means for deflecting the test piecebeam to the detector being provided on the measuring part. In addition,the device comprises a control/regulation unit at least for themotor-powered alignment of the optical unit relative to the referencestructure of the test piece by means of motor-powered adjustment of theangle of rotation of the retainer part and of the angle of rotation ofthe measuring part as a function of the position of the at least onepoint on the detector. For a more exact description of the individualelements of this device, reference may be made to the description of theknown theodolite test machine and of the device described above. Ofcourse, the method described can also be used with a device which has adifferent design but is substantially equivalent.

In the method according to the invention, the test piece is firstarranged on the retainer part. This is followed by preliminary alignmentof the optical unit and/or of the reference structure of the test pieceso that the test piece beam at least partly strikes the detector andproduces at least one point there. After the evaluation of the positionof this at least one point on the detector, in particular by thecontrol/regulation unit, fine alignment of the optical unit relative tothe reference structure is carried out by means of thecontrol/regulation unit as a function of the position of the at leastone point on the detector, so that the at least one point reaches acertain reference position. Then follows a determination of at least theangle of rotation of the retainer part and/or of the angle of rotationof the measuring part. Said test piece beam is formed by radiation whichis generated by the reference structure of the test piece or as modifiedby said reference structure with respect to a radiation parameter, forexample by reflection, scattering, refraction, stopping, filtration orshaping. The generation of the radiation is effected by means of anemitter which is in the form of, for example, a thermal or luminescenceemitter or in the form of a chemical or radioactive emitter. Since thetest piece beam which strikes the detector therefore arrives directly orindirectly from the reference structure of the test piece and does notoriginate from an auxiliary component, such as, for example, anauxiliary mirror, the reference structure can be aligned very preciselyrelative to the optical unit, or vice versa, since errors due to pooralignment of the auxiliary component relative to the reference structureare avoided. In addition, it is possible to choose referencestructures—for example in the form of an illuminated orself-illuminating mark—which can be mechanically coupled only withdifficulty, in particular components which are arranged in an opticallydetectable manner within a lens system. These are, for example, lenses,reticules, beam splitter cubes or an image recording surface within alens system.

This method is suitable, inter alia for checking or calibrating a testpiece equipped with an optical sighting unit, in particular a telescope,preferably a theodolite, a level or geodetic scanner, the opticalsighting unit being adjustable about a vertical axis and optionally atilting axis. An angle of rotation about a vertical axis and optionallyan angle of rotation about a tilting axis can be determined herewith.The optical sighting unit determines a sighting axis and has anoptically detectable mark, for example a reticule or a light exit. Alower part of the test piece is arranged on the retainer part so thatthe retainer part axis is substantially collinear with the vertical axisand optionally the measuring part axis is substantially collinear withthe tilting axis. Before, during or after the above mentionedpreliminary alignment of the optical unit, a preliminary alignment ofthe sighting unit of the test piece is carried out. By determining theangle of rotation about the vertical axis and/or optionally the angle ofrotation of the test piece about the tilting axis, checking orcalibration of a test piece can be effected by comparison with,respectively, the angle of rotation of the retainer part and the angleof rotation of the measuring part of the device.

In a possible general embodiment, the radiation is generated by anemitter arranged in the optical unit. Here, the optical unit has, inaddition to the emitter, a detector and a lens system for shaping theradiation emitted by the emitter and for focusing the test piece beam onto the detector. The lens system preferably has a variable focaldistance. The shaped radiation strikes a reflection surface to be testedwith respect to the alignment and formed by the reference structure ofthe test piece, and is reflected by said surface. The radiationreflected by the reference structure forms the test piece beam which isshaped by the lens system on appropriate alignment of the referencestructure relative to the optical unit, thus at least partly strikes thedetector and, on exact alignment, produces at least one point at acertain reference position on the detector. The reflecting referencestructure is—if required—possibly coated with a reflection-enhancingcoating or film. The emitter used is, for example, an LED, the radiationof which is fed via an optical fibre into the focal plane of the lenssystem. Depending on the application, a quadrant diode, a CCD imagesensor or another detector disclosed in the prior art can be used as adetector. If the reference structure serving as a reflection surface isa flat surface, the radiation emitted by the emitter is preferablycollimated by the lens system of the optical unit so that the test piecebeam is likewise collimated. In the case of a convex or concavereference structure which is formed, for example, by a lens surface ofthe test piece, the radiation is on the other hand shaped, in particularfocused or scattered, by the lens system of the optical unit inaccordance with the curvature, in particular the radius. If a lenshaving an antireflection coating is to be used as the referencestructure, the use of additional optical filters in the beam path of theradiation is advantageous. If the reference structure is a lens within alens system, for example a certain lens within a sighting unit, the useof optical filters may likewise be expedient.

It is also possible for the reference structure to be formed by anoptically detectable mark on the test piece or within the test piece,such as, for example, a reticule in the optical system of the sightingunit of the test piece, the radiation being modified with respect to aradiation parameter. This is effected in particular by illuminating areticule from the side of the objective or of the eye piece of theoptical sighting unit of the test piece by an emitter, optionally withthe use of optical filters, at least during the fine alignment of thedevice, this illumination forming the radiation. Here, the reticule isfocused by means of the objective of the sighting unit onto the detectorof the optical unit, with the result that the at least one point isproduced on the detector. Here, the emitter may either likewise bepresent in the optical unit or may be separately housed, for example inan additional optical unit which is present on that side of themeasuring part which is opposite the optical unit relative to themeasuring part axis.

It is furthermore possible to dispense with an emitter outside theoptical sighting unit of the test piece. This may be the case inparticular when the reticule is self-illuminating so that the reticuleitself produces the radiation, or if the reticule is illuminated by anemitter arranged in the optical sighting unit. The focusing of thereticule on to the detector is preferably effected by means of theobjective or by means of the eye piece. Self-illuminating reticules, forexample in the form of a luminescence emitter, are disclosed in theprior art.

If the test piece is a video theodolite, it is possible for thereference structure to be formed by the image recording surface of thetheodolite, in particular of the CCD chip, with the result that theorientation and a possible incorrect alignment of the image recordingsurface are measurable. Furthermore, the camera constant can be checked.

The beam splitter cube in a theodolite telescope can also serve as areference structure, with the result that the correct angular alignmentof a beam splitter cube can also be checked by means of the method.

If a laser telemeter is arranged in the test piece, the test piece beamcan be formed by a laser measuring beam emitted by the test piece. Thereference structure is thus formed by the laser diode. In this case, itis possible to compare an alignment of the optical axis of the testpiece with the alignment of the axis of the laser measuring beam and todetect possible deviation.

In addition, errors within the optical system of the sighting unit canbe determined by focusing a structure of at least one part of thesighting unit on to the detector by means of an emitter arranged on theside of the eye piece or the objective of the sighting unit of the testpiece. In the case of a focusable optical system, it is also possible toinvestigate the path of the focusing lens by means of the methoddescribed.

The use of an additional optical unit which is arranged on the side ofthe eye piece results in further possibilities. Like the optical unit,the additional optical unit may be in the form of an autocollimator or acamera for detecting the alignment relative to a reference structurewhich is formed by the eye piece itself or by a structure detectablefrom the side of the eye piece. Alternatively, the additional opticalunit may be in the form of an additional emitter which emits a beamwhich has certain optical properties—in particular three-dimensionalstructuring in the form of a certain pattern. After an interaction withat least one reference structure of the test piece, this beam isdetected by the opposite optical unit in the form of the test piecebeam. By comparing the optical properties—in particular thestructurings—of the beam emitted by the additional optical unit and ofthe test piece beam received by the optical unit, any optical errors inthe optical system of the test piece, for example inadequate opticaltelescope quality, any lens errors, aberrations or distortions andfocusing errors, are detected.

Below, the method according to the invention is described in more detailpurely by way of example in the form of specific embodiments partly withreference to devices and with the aid of figures. In the description ofthe figures, reference is made in some cases to reference numerals offigures already described before. Specifically,

FIG. 3 shows a diagram of an embodiment of the device for checking orcalibrating the angle-dependent alignment of a reference structure of ahigh-precision test piece having a measuring rocker mounted on one sideas a measuring part;

FIG. 4 shows a simplified sectional diagram of a first alternativeembodiment of the device having a measuring rocker mounted on one sideas a measuring part and a handling robot;

FIG. 5 shows a simplified sectional diagram of a second alternativeembodiment of the device having a measuring rocker mounted on one sideas a measuring part and a handling robot;

FIG. 6 shows a simplified sectional diagram of a third alternativeembodiment of the device having a measuring wheel mounted on one side asa measuring part and a handling robot;

FIG. 7 shows a simplified sectional diagram of a fourth alternativeembodiment of the device having a measuring ring mounted in the middlein the measuring plane as a measuring part;

FIG. 8 shows a schematic diagram of the beam path with a flat reflectionsurface as a reference structure of the test piece;

FIG. 9 shows a schematic diagram of the beam path with a convex lens asa reference structure of the test piece;

FIG. 10 shows a schematic diagram of the beam path with a reticule as areference structure of the test piece;

FIG. 11 shows a schematic diagram of the beam path with focusing of astructure within an optical sighting unit on to the detector.

FIG. 3 shows a possible embodiment of a device for carrying out themethod according to the invention. The device comprises a granite plinth2 which rests on a frame 24. The plinth 2 is composed of a plurality ofpart-elements which together approximately form an L-shape. A horizontalmeasuring unit 25 which has a retainer part 3 which is rotatable withhigh precision under motor power about a retainer part axis 4 pointingin the perpendicular direction is present on the plinth 2. The entiredevice can be inclined by adjusting the frame 24 so that the retainerpart axis 4 points exactly in the perpendicular direction, theinclination being monitored by means of an inclinometer (not shown). Therotatable mounting of the retainer part 3 is effected by means of aretainer part bearing unit 27 which is in the form of an air bearing. Anangle of rotation of the retainer part between the retainer part 3 andthe plinth 2 about the retainer part axis 4 is measurable with highprecision by means of a first angle encoder (not shown). A test piece 1in the form of a theodolite having an optical sighting unit 18 in theform of a telescope which is rotatable by means of an electric motorabout a vertical axis 20 and is tiltable by means of an electric motorabout a tilting axis 21 is fixed with the lower part 19 of its testpiece on the retainer part 3 by means of a fast-action connector 26, thevertical axis 20 of the test piece 1 coinciding with the retainer partaxis 4. A measuring part 5 in the form of a measuring yoke which has aU-shape and encompasses the retainer part axis 4 in the manner of tongsin the starting position shown is additionally rotatably arranged on theplinth 2. This measuring part 5 is supported axially and radially by ameasuring part bearing unit 6 in the form of an air bearing. Themeasuring part 5 is rotatable with high precision under motor powerrelative to the plinth 2 about a measuring part axis 7, an angle ofrotation of the measuring part about the measuring part axis 7 betweenthe measuring part 5 and the plinth 2 being measurable with highprecision by means of a second angle encoder (not shown). The measuringpart axis 7 and the tilting axis 21 lie in a common plane through whichthe retainer part axis 4 and the vertical axis 20 pass perpendicularly,this point of penetration forming the point of intersection between themeasuring part axis 7 and the tilting axis 21 of the test piece 1.Depending on the alignment of the test piece 1 relative to the retainerpart 4, the measuring part axis 7 and the tilting axis 21 may lie one ontop of the other which is the case in the diagram shown in FIG. 3. Thusit is possible to pivot the sighting unit 18 and the measuring part 5about a common axis. The measuring part bearing unit 6 is ahigh-precision air bearing which permits easy but stable pivoting of themeasuring part 5 about the measuring part axis 7 while maintaining verysmall tolerances. Since the measuring part bearing unit 6 is arranged onthe plinth 2 on a single side of a measuring plane 11 through which themeasuring part axis 7 passes perpendicularly and in which the retainerpart axis 4 lies, it is possible to adjust the measuring part bearingunit 6 exactly without resulting in distortions with a bearing unit onthe other side of the measuring plane 11 owing to staticoverdetermination. FIG. 3 schematically shows a small section of themeasuring plane 11. As a result of this design of the measuring part 5,which is substantially axially symmetrical with respect to the measuringpart axis 7, the centre of gravity of the measuring part 5 occurs afterthe measuring part axis 7. Consequently, the flexural and torsionalloads are substantially avoided and the drive of the measuring part 5 isrelieved so that tolerances are kept low and very high accuracies ofmeasurement are achievable. Present on the measuring part 5 is anoptical unit 8 having an optical detector (not shown in FIG. 3, seebelow), the optical unit 8 being arranged on the measuring part 5 sothat a test piece beam arriving from the direction of the test piece 1(not shown in FIG. 3, see below) can be received by the detector, whichtest piece beam lies substantially in the measuring plane 11 throughwhich the measuring part axis 7 passes perpendicularly and in which theretainer part axis 4 lies. In FIG. 3, the test piece beam is generatedby an illuminated reticule arranged in the sighting unit 18 (not shownin FIG. 3). In this case, the reticule is the reference structure, theangular alignment of which is to be checked. Here, the illuminatedreticule is focused by means of an objective 16 of the sighting unit 18on to the detector of the optical unit 8 and thus generates amultiplicity of points on the detector. The position of this image onthe detector changes with slight rotation of the retainer part 3 aboutthe retainer part axis 4 and of the test piece 1 about the vertical axis20 or of the measuring part 5 about the measuring part axis 7 and of thesighting unit 18 about the tilting axis 21. In the case of motor-poweredadjustment of the device and of the test piece 1 about the respectiveaxes, subsequent fine alignment, controlled by the position of the imageon the detector, and comparison of the respective measured angle values,it is thus possible to carry out checking of the angles in a highlyprecise manner. Here, a control/regulation unit 13 performs theevaluation of the detector of the optical unit 8 and the motor-poweredalignment of the optical unit 8 relative to the reference structure ofthe test piece 1 by means of motor-powered adjustment of the retainerpart 3 and of the measuring part 5 as a function of the position of theimage on the detector. In addition, the control/regulation unit 13performs the actuation of the alignment of the sighting unit 18 of thetest piece 1 by means of an electric motor and the determination and thevaluation of the measured angle values of the device and of the testpiece 1, the communication with the test piece 1 being effected by meansof a slip ring system (not shown) arranged in the retainer part 3 or bya radio link via Bluetooth. As can be seen in FIG. 3, it is not possiblein the embodiment shown to adjust the measuring part 5 in such a waythat the optical unit 8 is positioned close to the zenith. Adjustment ofthe measuring part 5 beyond the zenith is also not possible since thatpart of the measuring part 5 which is opposite the optical unit 8 wouldcollide with the horizontal measuring unit 25, and it is for this reasonthat penetration of the sighting unit 18 of the test piece 1 or ahorizontal angular adjustment is necessary for calibrating the oppositeangular range. However, this limitation is generally not disadvantageousin practice. Since positioning of the test piece 1 in exact alignmentwith the vertical axis on the horizontal measuring unit 25 is notpossible, a measurement close to the zenith would lead to incorrectresults, as described above in the description of the known theodolitetest machine. In addition, it is usually not possible for a userdirectly to carry out a measurement close to the zenith since the eyepiece of the sighting unit 18 is inaccessible in this region. However,embodiments in which measurement close to the zenith can also be carriedout are described further below.

FIG. 4 shows a simplified sectional diagram of a first alternativeembodiment of the device of FIG. 3. As in FIG. 3, the device forchecking a test piece 1 has a multi-part plinth 2 with a measuring partbearing unit 6 and a horizontal measuring unit 25 which comprises aretainer part bearing unit 27 and a retainer part 3 rotatable about theretainer part axis 4. The measuring part mounted on a single side of themeasuring plane 11 by the measuring part bearing unit 6 in the form ofan air bearing is in the form of a measuring rocker 5 a which has limbs5 a′, 5 a″ arranged at right angles to one another. The optical unit 8is arranged on one of these limbs 5 a′, 5 a″. The device also has ahandling robot 22 which comprises a robot plinth 29 and a gripper 28pivotable about the measuring part axis 7 by means of an electric motor.A mechanical connection can be produced between the gripper 28 and thesighting unit 18 of the test piece 1, in particular the objective 16, sothat the sighting unit 18 can be pivoted by means of the handling robot22. It is therefore possible to check a test piece which has noadjustment of its sighting unit by means of an electric motor, inparticular a mechanically adjustable theodolite, using the device, sincethe alignment of the test piece 1 is performed by the handling robot 22.Owing to a variable geometry of the gripper 28 test pieces of differentgeometries can be checked.

FIG. 5 shows a second alternative embodiment of the device of FIG. 3 insimplified form in a cut-out. The measuring part is in the form of ameasuring rocker 5 b, a substantial part of this measuring rocker 5 bbeing axially symmetrical with respect to the measuring part axis 7. Inaddition to the plinth 2, the measuring part bearing unit 6 arranged ona single side of the measuring plane 11 and in the form of an airbearing, the horizontal measuring unit 25, which comprises the retainerpart bearing unit 27 and the retainer part 3 rotatable about theretainer part axis 4, and the handling robot 22 with the robot plinth29, the test piece 1 is shown with the optical sighting unit 18including an eye piece 23. In addition to the optical unit 8, anadditional optical unit 15 is arranged on the measuring rocker 5 b, onthat side which is opposite the optical unit 8 with respect to themeasuring part axis 7. This additional optical unit 15 is in the form ofan additional emitter which generates a radiation 30 which illuminates areticule (not shown) in the sighting unit 18 on the side of the eyepiece 23. The reticule modifies the radiation 30 with regard to aradiation parameter by stopping, this modified radiation forming thetest piece beam 10 which leaves the sighting unit 18 via the objective16, is picked up by the optical unit 8 and produces at least one pointon the detector (not shown in FIG. 5). Alternatively, it is possible toform the additional optical unit 15 as an additional mirror. In thiscase, the radiation is, for example, emitted by the optical unit 8,reflected by the additional mirror and modified by the reticule withregard to a radiation parameter, this modification taking place eitherbefore, after or before and after the reflection at the additionalmirror, and then strikes the detector. It is furthermore possible forthe additional optical unit 15 to emit a radiation 30 having astructuring—for example a pattern. Particularly by comparison of thestructuring of the emitted radiation 30 and of the received test piecebeam 10 by means of image processing, errors in the optical system ofthe sighting unit 18, in particular lens errors, aberrations,distortions, focusing errors in the tube, etc. can be detected.

FIG. 6 shows a simplified sectional diagram of a third alternativeembodiment of the device with a measuring part in the form of measuringwheel 5 c. The measuring wheel 5 c is mounted on the measuring partbearing unit 6 arranged on a single side of the measuring plane 11 andin the form of an air bearing so as to be rotatable about the measuringpart axis 7. As in the above designs, the device has a horizontalmeasuring unit 25 with a retainer part bearing unit 27 for mounting theretainer part 3 so as to be rotatable about the retainer part axis 4.Furthermore, the test piece 1 with its sighting unit 18 and theobjective 16, positioned on the retainer part 3, and the handling robot22 with the robot plinth 29, can be seen. Owing to the geometry of themeasuring wheel 5 c, the device on the other hand has a plinth 2 a whichis formed so that the measuring wheel 5 c encloses the test piece 1 andthe horizontal measuring unit 25. Both the optical unit 8 and, on theopposite side, the additional optical unit 15 are arranged on themeasuring wheel 5 c. The rotationally symmetrical shape of the measuringwheel 5 c has the advantage that elastic deformations which occur as afunction of the position of the optical unit 8 and the additionaloptical unit 15 can be substantially avoided. In this embodiment,measurements close to the zenith—in particular while dispensing with theadditional optical unit 15—can be carried out since the measuring wheelis substantially freely rotatable—with appropriate positioning of theoptical unit 8.

While, in the preceding exemplary embodiments, the measuring partbearing unit is present on a single side of the measuring plane 11, FIG.7 shows an embodiment in which the measuring part bearing unit isarranged within the measuring plane 11. The horizontal measuring unit 25fixed on a plinth 2 b and having a retainer part bearing unit 27 forrotatable mounting of the retainer part 3 about the retainer part axis 4corresponds to the preceding description. The test piece 1 with itssighting unit 18, the eye piece 23 and the objective 16, positioned onthe retainer part 3, has an illuminated reticule (not shown in FIG. 7),the emitted radiation of which forms the test piece beam 10 aftershaping by the objective 16. The test piece 1 and the horizontalmeasuring unit 25 are enclosed by an annular measuring part in the formof measuring ring 5 d. The measuring ring 5 d which is rotationallysymmetrical in its basic form is mounted so as to be rotatable about themeasuring part axis 7, mounting being effected by means of a measuringpart bearing unit 6 a which is in the form of an air bearing and isarranged on and partly in the multi-part plinth 2 b. The outer surfaceand optionally also the inner surface of the measuring ring 5 d arebearing surfaces of the air bearing here. An optical unit 8 mounted onthe measuring ring 5 d and having an optical detector (not shown in FIG.7) serves, as already described above, for receiving the test piece beam10, by means of which the reticule is focused on to the detector of theoptical unit 8 and thus produces a multiplicity of points there.Similarly to FIG. 5 and FIG. 6, it is also possible to equip themeasuring ring 5 d with an additional optical unit 15, in particular anadditional emitter or an additional mirror. Since the measuring partbearing unit 6 a is arranged in the middle and is present in themeasuring plane 11, below the test piece 1 and below the horizontalmeasuring unit 25, the test piece 1 is easily accessible from bothsides, which is advantageous particularly during the mounting of thetest piece 1 and calibration work on the test piece 1. Owing to therotationally symmetrical basic shape of the measuring ring 5 d and themeasuring part bearing unit 6 a present close to or in the perpendicularof the centre of gravity of the measuring ring 5 d, flexural andtorsional moments on the measuring part are substantially avoided, sothat very high accuracies of measurement can be achieved.

FIG. 8 shows the beam path of a possible embodiment in which the opticalunit has the design of a known autocollimator and the referencestructure of the test piece is formed by a flat reflection surface. Theoptical unit 8 a in the form of an autocollimator comprises an emitter31 a, an optical unit mark 32 in the form of a reticule, a beam splittercube 33 for physical beam splitting, an optical unit objective 34 a andan optical detector 9. The optical unit 8 a emits radiation in the formof a collimated emitted beam 35 a, which is reflected by a flatreflection surface 36 on the test piece 1, which reflection surfaceforms the reference structure. This reflected beam which is thereforemodified with respect to a radiation parameter forms the test piece beam10 a, which is therefore likewise collimated. If the collimated emittedbeam 35 a strikes the flat reflection surface 36 substantiallyperpendicularly, the test piece beam 10 a is picked up by the opticalunit objective 34 a and focused on to the detector 9, on which an imageof the optical unit mark 32 is therefore produced and at least one point12 or a family of such points 12 is produced on the detector 9. Theposition of this image and of this family of points 12 is dependent onthe angular alignment of the optical unit 8 a relative to the flatreflection surface 36 or the reference structure of the test piece 1.This flat reflection surface 36 is formed directly by a flat reflectionsurface as a reference structure on the test piece 1. It is herebypossible also to investigate a polygonal mirror, for example a referencemirror to be used for the rosette method, with regard to the alignmentof its mirror surfaces.

However, the reference structure of numerous test pieces which is to beinvestigated with regard to the angular alignment is often not—asabove—formed by a flat surface but by a curved structure, for example alens present within the objective 16 of the sighting unit 18. FIG. 9shows the optical unit 8 a—as also FIG. 8. However, an additionalauxiliary lens 37 a changeable in its position and in the form of ascattering lens is present before the optical unit objective 34 a, sothat the emitted beam 35 b diverges. The divergent emitted beam 35 bstrikes a first and a second collecting lens 38 a′ and 38 a″ of theobjective 16 of the optical sighting unit 18 of the test piece 1, isfocused by these collecting lenses 38 a′ and 38 a″, strikes the convexlens 39, which forms the reference structure of the test piece 1 here,and is reflected by this convex lens 39, with the result that a changeof radiation parameter takes place. The reflected beam forms the testpiece beam 10 b, which is focused as described above on to the detector9 of the optical unit 8 a. In order that the main reflection of thetransmitted beam 35 b takes place at the convex lens 39—and not at apreceding lens—the use of optical filters (not shown in FIG. 9), whichare arranged after the emitter 31 a, is possible. The checking of theangular alignment by the optical unit 8 a is effected in the mannerdescribed above. It is possible to convert the device by flexible use ofthe auxiliary lens 37 a from a flat to a convex or optionally a concavereference structure without substantially intervening in the device. Thedesign of the auxiliary lens depends in particular on the form of thelens serving as a reference structure and on the preceding lens system.

In a further embodiment, as shown in FIG. 10, the reference structure isformed by a reticule in the sighting unit of the test piece. The opticalunit 8 b has an emitter 31 b, a beam splitter cube 33 for physical beamsplitting, an optical unit objective 34 b and an optical detector 9. Theoptical unit Bb emits radiation in the form of a transmitted beam 35 cwhich is picked up by the objective 16 of the sighting unit 18 of thetest piece 1, strikes the reticule 14 of the sighting unit 18 andilluminates this reticule 14. The reticule 14 is present at the focalpoint of the objective 16 of the sighting unit 18. The reflection causedby this illumination of the reticule 14 forms a beam which, aftercollimation by said objective 16, represents the test piece beam 10 c.This test piece beam 10 c is focused by the optical unit objective 34 bon to the detector 9, on which an image of the reticule 14 of thesighting unit 18 of the test piece 1 is thus produced, and produces afamily of points 12 there. The position of this image or of the familyof these points 12 on the detector 9 is dependent on the angularalignment of the sighting unit 18 or of the reticule 14 as a referencestructure of the test piece 1 relative to the optical unit 8 b of thedevice. Alternatively, it is possible, for example, not to illuminatethe reticule 14 via the objective 16 by means of an emitter 31 b withinthe optical unit 8 b but to carry out the illumination on the other sideof the reticule on the eye piece 23 side (cf FIG. 5 and FIG. 7) of thesighting unit 18, for example via an additional optical unit 15 (cfFIGS. 5 and 6) in the form of an additional emitter. In the case of aself-illuminating reticule or of a reticule illuminated by illuminationwithin the sighting unit 18, an external emitter can be completelydispensed with. Further possibilities for illuminating the reticule 14are also possible, where illumination is also to be understood asmeaning exposure to a non visible radiation. Instead of the reticule 14,the surface of a beam splitter cube of the sighting unit, of an imagerecording surface or of a distance-measuring laser diode can also serveas the reflection surface.

If it is intended to investigate a structure or an object, for example areticule or an aperture, within the sighting unit 18, this can beeffected in the manner described in FIG. 11. The optical unit 8 c has anemitter 31 c, a beam splitter cube 33 for physical beam splitting, anoptical unit objective 34 c and an optical detector 9. Radiation in theform of a transmitted beam 35 d is scattered by the auxiliary lens 37 band illuminates a structure 40 within the optical sighting unit 18 ofthe test piece 1. This illuminated structure 40 is focused by means ofthe collecting lenses 38 b′ and 38 b″, the auxiliary lens 37 b and theoptical unit objective 34 c on to the detector 9 by means of the beam 10d and can thus be represented graphically and checked. This structure isformed, for example, by an image recording surface, for example aCCD-chip, or a laser diode of a telemeter. Other illumination variants,as already described above, can also be realised here.

It is possible to carry out the test methods described in FIG. 8 to 11with a single optical unit, optionally with use of different objectivesor auxiliary lenses, and thereby to use a single device withoutcomplicated conversion for different test pieces or test methods.

1. Method for checking or calibrating the angle-dependent alignment of areference structure of a high-precision test piece, using a devicecomprising an adjustable or fixed retainer part for retaining the testpiece an adjustable measuring part, the measuring part and the retainerpart being rotatable relative to one another about a retainer part axisand a measuring part axis intersecting the retainer part axis at rightangles, and an angle of rotation of the retainer part about the retainerpart axis and an angle of rotation of the measuring part about themeasuring part axis between the measuring part and the retainer partbeing measurable, an optical unit arranged on the measuring part andhaving an optical detector for receiving at least one test piece beamwhich interacts with the test piece and runs substantially in ameasuring plane, through which the measuring part axis passesperpendicularly and in which the retainer part axis lies, and producesat least one point on the detector, and a control/regulation unit atleast for the motor-powered alignment of the optical unit relative tothe reference structure of the test piece by means of motor-poweredadjustment of the axis of rotation of the retainer part and of the axisof rotation of the measuring part as a function of the position of theat least one point on the detector comprising the method stepsarrangement of the test piece on the retainer part, preliminaryalignment of the optical unit and/or of the reference structure of thetest piece so that the test piece beam at least partly strikes thedetector and produces at least the one point there, evaluation of theposition of the at least one point on the detector by thecontrol/regulation unit, relative fine alignment of the optical unitrelative to the reference structure by means of the control/regulationunit as a function of the position of the at least one point on thedetector so that the at least one point reaches a certain referenceposition on the detector and determination of at least the angle ofrotation of the retainer part and/or of the angle of rotation of themeasuring part, radiation being produced by the reference structure ofthe test piece or being modified with respect to a radiation parameter,in particular by reflection, stopping, filtration or shaping, and theproduced or modified beam forming the test piece beam.
 2. Methodaccording to claim 1, the test piece in particular a theodolite, a levelor a geodetic scanner—having an optical sighting unit which isadjustable about a vertical axis and optionally a tilting axis,determines a sighting axis and has an optically detectable mark, forexample a reticule or a light exit, an angle of rotation of the verticalaxis and optionally an angle of rotation of the tilting axis beingdeterminable, and a test piece lower part being arranged on the retainerpart so that the retainer part axis is substantially collinear with thevertical axis and optionally the measuring part axis is substantiallycollinear with the tilting axis, a preliminary alignment of the opticalsighting unit being effected before or during the preliminary alignmentof the optical unit, and the angle of rotation of the vertical axisand/or optionally the angle of rotation of the tilting axis beingdetermined.
 3. Method according to claim 2, the radiation being emittedand shaped by an emitter arranged in the optical unit, the radiationthen being reflected by the reference structure of the test piece andthe test piece beam thus being formed, and the test piece beam beingfocussed on to the detector on striking a part of the optical unit and,in the case of exact alignment of the optical unit relative to thereference structure, producing at least one point on the detector. 4.Method according to claim 3, the reference structure being formed by alens of the sighting unit.
 5. Method according to claim 3, the referencestructure being formed by a beam splitter cube of the sighting unit. 6.Method according to claim 3, the reference structure being formed by animage recording surface—in particular a CCD chip—of the sighting unit.7. Method according to claim 2, the reference structure being formed bythe optically detectable mark which is illuminated actively or passivelyat least during the fine alignment, and the radiation being produced bythe mark or modified with respect to the radiation parameter.
 8. Methodaccording to claim 7, the mark being in the form of a reticule, whichreticule is self-illuminating or is illuminated, at least during thefine alignment, by an emitter arranged in the optical sighting unit, thetest piece beam thus formed being focussed directly or indirectly atleast partly on to the detector by means of an objective of the sightingunit and thus producing the at least one point on the detector. 9.Method according to claim 7, the mark being in the form of a reticuleand being illuminated, at least during the fine alignment, by means ofan emitter arranged on the side of an objective of the sighting unit,the reticule being focussed directly or indirectly at least partly on tothe detector by means of the objective of the sighting unit and thusproducing the at least one point on the detector.
 10. Method accordingto claim 7, the mark being in the form of a reticule and beingilluminated, at least during the fine alignment, by means of anadditional emitter arranged on the side of an eyepiece of the sightingunit, in particular by means of an additional optical unit, the reticulebeing focused directly or indirectly at least partly on to the detectorby means of an objective of the sighting unit and thus producing the atleast one point on the detector.
 11. Method according to claim 2, theradiation being emitted in the direction of the eye piece by anadditional optical unit arranged on the side of an eye piece or of anobjective of the sighting unit and having a three-dimensionalstructuring, in particular in the form of a pattern, the radiationpassing through the sighting unit, being modified by at least onereference structure in the sighting unit with respect to a radiationparameter and thus forming the test piece beam, and the test piece beam,after emergence from the objective or eye piece of the sighting unit,being focused on to the detector on striking a part of the optical unit,and producing a multiplicity of points on the detector, and opticalerrors, in particular aberrations and distortions, being detectable byevaluation of the multiplicity of points, detected by the detector, bythe control/regulation unit.
 12. Method according to claim 2, astructure of at least a part of the sighting unit being focused on tothe detector.
 13. Method according to claim 1, the test piece having alaser telemeter with a laser measuring beam emitter forming thereference structure and intended for producing a laser measuring beamwhich forms the test piece beam, comprising the additional method stepof emission of a laser measuring beam by the laser telemeter.
 14. Methodaccording to claim 1, the test piece being heated at least from one sideby a thermal emitter for determining the thermal behaviour.